The distribution of Schistosoma japonicum eggs in faeces and the effect of stirring faecal specimens

Sources of variability in the measurement of Ascaris lumbricoides infection intensity by Kato-Katz and qPCR

Background

Understanding and quantifying the sources and implications of error in the measurement of helminth egg intensity using Kato-Katz (KK) and the newly emerging “gold standard” quantitative polymerase chain reaction (qPCR) technique is necessary for the appropriate design of epidemiological studies, including impact assessments for deworming programs.

Methods

Repeated measurements of Ascaris lumbricoides infection intensity were made from samples collected in western Kenya using the qPCR and KK techniques. These data were combined with data on post-treatment worm expulsions. Random effects regression models were used to quantify the variability associated with different technical and biological factors for qPCR and KK diagnosis. The relative precision of these methods was compared, as was the precision of multiple qPCR replicates.

Results

For both KK and qPCR, intensity measurements were largely determined by the identity of the stool donor. Stool donor explained 92.4% of variability in qPCR measurements and 54.5% of observed measurement variance for KK. An additional 39.1% of variance in KK measurements was attributable to having expelled adult A. lumbricoides worms following anthelmintic treatment. For qPCR, the remaining 7.6% of variability was explained by the efficiency of the DNA extraction (2.4%), plate-to-plate variability (0.2%) and other residual factors (5%). Differences in replicate measurements by qPCR were comparatively small. In addition to KK variability based on stool donor infection levels, the slide reader was highly statistically significant, although it only explained 1.4% of the total variation. In a comparison of qPCR and KK variance to mean ratios under ideal conditions, the coefficient of variation was on average 3.6 times larger for KK highlighting increased precision of qPCR.

Conclusions

Person-to-person differences explain the majority of variability in egg intensity measurements by qPCR and KK, with very little additional variability explained by the technical factors associated with the practical implementation of these techniques. qPCR provides approximately 3.6 times more precision in estimating A. lumbricoides egg intensity than KK, and could potentially be made more cost-effective by testing each sample only once without diminishing the power of a study to assess population-level intensity and prevalence.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2164-y) contains supplementary material, which is available to authorized users.

Detection of Schistosoma mansoni antibodies in a low-endemicity area using indirect immunofluorescence and circumoval precipitin test

Parasitological diagnostic methods for schistosomiasis lack sensitivity, especially in regions of low endemicity. The objective of this study was to determine the prevalence of Schistosoma mansoni infections by antibody detection using the indirect immunofluorescence assay (IFA-IgM) and circumoval precipitin test (COPT). Serum samples of 572 individuals were randomly selected. The IFA-IgM and COPT were used to detect anti-S. mansoni antibodies. Of the patients studied, 15.9% (N = 91) were IFA-IgM positive and 5.1% (N = 29) had COPT reactions (P < 0.001 by McNemar's test). Immunodiagnostic techniques showed higher infection prevalence than had been previously estimated. This study suggests that combined use of these diagnostic tools could be useful for the diagnosis of schistosomiasis in epidemiological studies in areas of low endemicity.

Detection of Schistosoma mansoni infection by TaqMan® Real-Time PCR in a hamster model

An experimental study in hamsters was performed to evaluate the capability for detecting Schistosoma mansoni DNA in serum and fecal samples during the pre and post-egg-laying periods of infection using TaqMan® Real-Time PCR system (qPCR), was compared with the circumoval precipitin test (COPT) and the Kato-Katz technique, especially among individuals with low parasitic burden. Twenty-four hamsters were infected with cercariae. Three hamsters were sacrificed per week under anesthesia, from 7 days post infection (DPI) up to 56 DPI. A serum sample and a pool of feces were collected from each hamster. The presence of S. mansoni eggs in fecal samples was evaluated by Kato-Katz method and in the hamsters gutby histopathology. Detection of S. mansoni DNA was performed using qPCR and S. mansoni antibody using COPT. The first detection of eggs in feces by Kato-Katz method and S. mansoni DNA in feces by qPCR occurred 49 DPI. Nevertheless, S. mansoni DNA was detected in serum samples from 14 up to 56 DPI. COPT was positive at 35 DPI. The results not only confirm the reliability of S. mansoni DNA detection by qPCR, but also demonstrate that serum is a trustworthy source of DNA in the pre patent infection period.

Comparison of the performance of two spontaneous sedimentation techniques for the diagnosis of human intestinal parasites in the absence of a gold standard

Performance evaluation of diagnostic tests is critical in the search for accurate diagnoses. A gold standard test is usually absent in parasitology, thus rendering satisfactory assessment of diagnostic accuracy difficult. Moreover, reliability (assessed by the study of repeatability) is a rarely studied characteristic of diagnostic tests. This study compared and evaluated the performance (repeatability, concordance and accuracy) of the spontaneous sedimentation technique (SST) and the Paratest for the diagnosis of Giardia lamblia, Entamoeba histolytica complex, Blastocystis spp., Ascaris lumbricoides, hookworm, Trichuris trichiura and Calodium hepaticum. Fecal samples of 143 individuals were separated into three replicates for each test. Concordance and homogeneity of the results between replicates of each test and between tests were evaluated. Proportions of positives, sensitivity and specificity were estimated using a Bayesian Latent Class Model. High repeatability of both tests was found for the detection of intestinal parasites, except for Blastocystis spp. and hookworm. Concordance between tests was generally high (concordance correlation coefficient, 0.72-0.88), except for Blastocystis spp., hookworm and T. trichiura. The Paratest detected more cases of Blastocystis spp. and fewer of hookworm than the SST. The tests were quite discordant in the detection of T. trichiura. A low sensitivity (39.4-49.2% for SST, 35.8-53.8% for Paratest) and a high specificity (93.2-97.2%) were found for both tests. The Paratest presented a slightly higher sensitivity for the diagnosis of Blastocystis spp. (53.8%), and SST did so for hookworm (49.2%). This is the first study on repeatability and accuracy (using a Bayesian approach) of two spontaneous sedimentation techniques. These results suggest underdiagnosis of little dense parasitic forms due to technical limitations in both tests. We conclude that the combined study of repeatability, concordance and accuracy is a key strategy for better evaluation of the performance of tests and is also useful for the identification of technical limitations.

An in-depth analysis of a piece of shit: distribution of Schistosoma mansoni and hookworm eggs in human stool

Background

An accurate diagnosis of helminth infection is important to improve patient management. However, there is considerable intra- and inter-specimen variation of helminth egg counts in human feces. Homogenization of stool samples has been suggested to improve diagnostic accuracy, but there are no detailed investigations. Rapid disintegration of hookworm eggs constitutes another problem in epidemiological surveys. We studied the spatial distribution of Schistosoma mansoni and hookworm eggs in stool samples, the effect of homogenization, and determined egg counts over time in stool samples stored under different conditions.

Methodology

Whole-stool samples were collected from 222 individuals in a rural part of south Côte d'Ivoire. Samples were cut into four pieces and helminth egg locations from the front to the back and from the center to the surface were analyzed. Some samples were homogenized and fecal egg counts (FECs) compared before and after homogenization. The effect of stool storing methods on FECs was investigated over time, comparing stool storage on ice, covering stool samples with a water-soaked tissue, or keeping stool samples in the shade.

Principal Findings

We found no clear spatial pattern of S. mansoni and hookworm eggs in fecal samples. Homogenization decreased S. mansoni FECs (p = 0.026), while no effect was observed for hookworm and other soil-transmitted helminths. Hookworm FECs decreased over time. Storing stool samples on ice or covered with a moist tissue slowed down hookworm egg decay (p<0.005).

Conclusions/Significance

Our findings have important implications for helminth diagnosis at the individual patient level and for epidemiological surveys, anthelmintic drug efficacy studies and monitoring of control programs. Specifically, homogenization of fecal samples is recommended for an accurate detection of S. mansoni eggs, while keeping collected stool samples cool and moist delayed the disintegration of hookworm eggs.

An accurate diagnosis of parasitic worm (helminth) infections is important for adequate patient treatment and disease control programs. Helminth eggs in human stool samples are used as an indicator of infection intensity and morbidity. However, little is known about the exact distribution of helminth eggs in stool samples. Homogenization has been suggested to improve the diagnostic accuracy. Hookworm eggs disintegrate over time, which makes their detection challenging in epidemiological surveys. We determined the location of helminth eggs in entire stool samples from 222 individuals in Côte d'Ivoire. We also investigated whether homogenization has an effect on the detection of eggs, and determined egg counts over time in stool samples stored on ice, covered with a moist tissue, or kept in the shade. No clear pattern of helminth egg distribution was found in human stool samples. Homogenization resulted in more accurate egg counts of the blood fluke Schistosoma mansoni, while it did not affect other helminths. Keeping stool samples on ice or covered with a wet tissue slows down the disintegration of hookworm eggs. Our findings have important implications for individual patient management and the design and implementation of epidemiological surveys and helminth disease control programs.

Detection of circulating antigen in serum of mice infected with Schistosoma japonicum by immunomagnetic bead ELISA based on IgY

We developed a novel immunomagnetic bead ELISA based on IgY (egg yolk immunoglobulin) for detection of circulating antigen (CA) in sera of mice infected with Schistosoma japonicum. The assay involved the use of chicken polyclonal antibodies IgY against soluble egg antigens (SEA) of S. japonicum as a capture antibody and anti-SEA mouse monoclonal antibody NP28-5B labeled horseradish peroxidase (HRP) as a detecting antibody. Two groups of BALB/c mice infected with S. japonicum cercariae were used: lightly infected mice (infected with 10 S. japonicum cercariae) and heavily infected mice (infected with 30 S. japonicum cercariae). The CA was detectable as early as 4 and 5 weeks after infection in the sera of heavily and lightly infected mice, respectively. The CA levels rose rapidly and reached a peak in 8 weeks after infection and then remained a plateau for at least another 6 weeks in both groups. Moreover, the effect of praziquantel on the CA levels was also investigated. The heavily infected mice were treated with praziquantel and the CA levels in sera increased dramatically in the first week post-treatment and then decreased to the control level by 6 weeks after treatment. The novel assay appears to be sensitive for detection of schistosomal antigenemia and valuable to judge the efficacy of chemotherapy in murine schistosomiasis.

Development and evaluation of a Western blot kit for diagnosis of schistosomiasis

We evaluated the performance of Western blot (WB) analysis using commercially available antigen strips and compared the results with those of indirect hemagglutination (IHA) and indirect immunofluorescence (IFAT) for the serodiagnosis of human schistosomiasis. The antigen preparation was a crude extract of Schistosoma mansoni. The WB profile characteristics of schistosomiasis were characterized by comparing the results for 58 serum samples from patients with parasitologically proven S. mansoni (n = 12) and S. haematobium (n = 46) infections and 37 individuals with probable cases of schistosomiasis but with only positive serology results. The specificity of WB analysis was assessed by testing 12 serum samples from healthy subjects, 67 serum samples from patients with other proven helminthic and protozoan infections, and 16 serum samples from patients with autoantibodies. Six immunodominant bands (65, 70, 80, 95, 110, and 120 kDa) were revealed with sera from patients with schistosomiasis. The presence of three or more bands in the range 65 to 120 kDa, with the exception of the 100-kDa band, was considered diagnostic for Schistosoma infection and had a specificity of 100% in our series. In patients with proven schistosomiasis, the sensitivity of WB analysis was 84.5%, whereas those of IFAT and IHA were 65.5 and 72.9%, respectively. For serologically proven cases, the sensitivity of WB analysis was 97.3%. The overall sensitivity and specificity for both groups of patients were 89.5 and 100%, respectively, with positive and negative predictive values of 100 and 91.3%, respectively. We conclude that WB analysis is a useful technique for the immunological diagnosis of schistosomiasis.

Copro-PCR based detection of Schistosoma eggs using mitochondrial DNA markers

We report on a sensitive, specific and easy to interpret PCR based diagnostic tool for the detection of Schistosoma japonicum eggs in the faeces of infected mammalian hosts. Primer pairs were designed to amplify regions of the mitochondrial DNA of the parasite. The specificity of the PCR primers was tested using either faecal samples from non-infected hosts or hosts infected with the related schistosome species S. mansoni. Sensitivity was investigated in a study, which differentiated the presence or absence of eggs in faecal samples. PCR results were correlated with analysis of the samples by microscopy. PCR analysis provided a level of sensitivity of 87.7%, while specificity was 100%. The PCR-based assay could detect mitochondrial DNA from as little as 0.3 of a single egg. The overall detection threshold of the PCR test was >or=60 eggs per gram of faeces. Advantages of this technique include the ability to scale-up screening and the reproducibility and simplicity of interpretation of results compared with standard microscopic methods.